What is first argument in parameterless constructor?

I have simple program like this:

public class Foo
{
    public Foo()
    {
    }
    public int MyInt { get; set; } = 10;
    public List<int> MyList { get; set; } = new List<int>();
}

public class Program
{
    static public void Main()
    {
        Console.WriteLine(new Foo().MyInt);
        Console.ReadLine();
    }
}

I decided to see il code of such program (I am interested in Foo's constructor). Here is it:

.method public hidebysig specialname rtspecialname 
        instance void  .ctor() cil managed
{
// Code size       26 (0x1a)
.maxstack  8
IL_0000:  ldarg.0
IL_0001:  ldc.i4.s   10
IL_0003:  stfld      int32 Foo::'<MyInt>k__BackingField'
IL_0008:  ldarg.0
IL_0009:  newobj     instance void class [mscorlib]System.Collections.Generic.List`1<int32>::.ctor()
IL_000e:  stfld      class [mscorlib]System.Collections.Generic.List`1<int32> Foo::'<MyList>k__BackingField'
IL_0013:  ldarg.0
IL_0014:  call       instance void [mscorlib]System.Object::.ctor()
IL_0019:  ret
} // end of method Foo::.ctor

I wondered, when I saw second line - ldarg.0. What does it mean? this pointer? but object was not created yet. How can I modify its members? My assumption is that before calling constructor, clr firstly allocates memory for object. Then initializes members to default values, then invokes constructor. Another interesting moment that object calling is last. I thought that it will be first.